Manufacture of gel compositions



i atented Apr. 25

Otis W. -A1h;'n,'EaZSt"R0int, Ga., assignor to Inter- ;nat qnakM ne ais C m al Gorpo at m a corporation of N ew York No Drawing. g milication 'siithflier 35W,

This invention relates to an *improvedprocess for "the hydration of hygroscopic "compositions which 'decrepitat'e when in contact With'fiiquid water. More particularly, the invention relates to an improved process for the hydration of the aforesaid compositions; followedby impregnating the hydrated -eompositions=cwith' an impregnating agent.

Hygroscopic compositions 'such as synthetic metal 1 oxide gels and the like, which maycoI-rtain either "one or a'plurality 'of' metal oxidesa-re used for a wide variety of'pu-rposes; amongtvhich may bementioned' dehydrating agents inirefrigoration; systems, dehur'nidifying apparatus and dessicants for pa-ckaged materials. fSuch gel's are also 7 useful Y as bases .ior catalysts :which are employed in the petroleum industry in "suchrprocesses as the cracking,hydroforming,alkylation and polymerization of hydrocarbons; :Iheebnven tional method "of "preparing such metal "oxide gels involves adding anacidic solution which-may or may, not contain a metal salt: to an' a'l kali nes'olution which usually contains a metal-containing anion; resulting in the precipitation of meta-l *ox=- ide-hydrogels. For example, asilicicacid-gel which a maybe use'd tomanufacture either a-dessicant material 'or a catalyst' support may be prepared by mixing hydrochloric acid orfsMlfuiic-aci'd solution with a solution of sodium silicate or water-glass and permitting the resulting-solutioneto'istand until the silicic acid precipitates "or :forms a co- .hesive gel The structureofthe-hydrogel as Well as-that of t-he'vultimate anhydrous product which is tobe produced will depend uponthe'conc'entra :tion of the reactantanpongthe "temperature-of the gelation reaction, upon the .pH oft-he result-ant admixed solutions, and upon-the time required-for gelati-on. Hydrogels containing either 'one or-"a plurality of -;metal oxides such as igels comprising precipitated oxides :of iron, aluminum vanadium, copper, manganese, chromiumpr mixtures ofsaid oxides are prepared by admixing appropriate acidic and basic solutions-containing salts of sue'h metals. The resultant precipitated hydrogel --is usually dehydratedby gbreaking the-'hydrogelinto particles of suitable size and'dryingthe same at elevated temperatures, usually above-200 F.

It has been standard practice toimpreg-nate the substantially anhydrous gel prod-ucts nescribed above -by adding thereto an aqueous solution of a composition which is eapable of': being converted into a different catalyticsubstance, usually by heating or calciningthe V-irnpregnated e'l'atfelevated temperatures. Y'For example, a solution of aluminum ni'trafte o'r aluminumchlo- 2 ride may be added to anhydrous silica gel, apermitting the resultant "mixture to :stand until-a suitableamount 'ofaluminum. compound has been absorbed by the gel. The-resulting impregnated, hydrated gel :is then heated at elevated temperartu res, whereuponl the aluminum salt decomposes into 'a'lum"mum1oxide whichi'r'emains precipitated in the-:gel'strueture' while the l=cationic portion of the aluminum salt is converted into volatile ases such as'roxidesvof nitrogen, andhydrogen chloride. 'Othersoluble salts ofsu'ch'metals as copper, zine,-zz-platinum, rnanganese and-chrom ium may b'egireoipitatedingel structures in a :similar manner in order to produce aparticular catalytic substance. -'='l-his vdryirrg or calcining operation usuallyresultsin a-s'ubstantial shrinkage of the hydrogel particles and results in a wproduct in which internal'astres'ses and strains have been set up. It-is :genera'llyiknownthat uponadding esueh aqueous solutionsft ubstanti-al ly anhydrous metal oxidesgelssuch as silica gel, the gel absorbs thei im' oregnatingsolution sox rapidly that the gel particles-are shattered, thereby-:greatlyredueing thesi-ze of the gel iparticles. :This requires a further =sizing= operation= following the ultimate ealcining steprand results in-the lossef a substantial; amoun "'of the original :lgel product due to the -;fines which are produced as :a :result of the shatteni-ng of the gel. :It;hasq beenzproposed previously' to circumvent; this particular difii'culty by only partially ;-dehy'drating the original upreci pitated-vhydrogel, .ior example, :until the moisture eontent of the hydrogel has :been reduced toi between about zfl and about ififljrby weigh-t. Sueh procedures are described in -patents issued to. Pat- ;riek, No.;1;695-,'14 0, and,toMcKinnemNo:2,147,985. However,-i-thasbeeniobservedthat-when partially dried hydrogels {are impregnated;with-aqueous solutions of metallic salts ofthe-type herein previously ties cribed, and the resultant --impregnated hydrogel is then further dried; to :9, moisture conen ef etwee a and about 7% by weight, on r pr Qi -ble u of, ri a of the hy ro gelparticles ocours; resultin in a product whose ea t ole s em erit a th t of th v roe l be n imr eena ed- 'hQ Q SO'b Q l proposedto subject sabsta-ntiallyanhydrous silica gel or other metal goiridegelspf tl -1 e type herein -.previously described to the-action--of a;mixture ofstea'm and air. Such-a process is described in 'a patent issued tostoewener; No. 1 798 766. This process requires a substantial investment inprocessi-ng equipment and: -a reasonable amount of; care mustbesexer- (aisedxi-n order; to: prevent condensation; of water in thersteamfohambers upontherdrygel. -Such condensation would cause the shattering or decrepitation of the gel, which is objectionable for the reasons hereinbefore set forth.

It is an object of the invention to provide an improved process for the hydration of hygroscopic compositions which decrepitate when in contact with liquid Water, and to minimize such decrepitation.

It is a further object of the invention to provide an improved process for the hydration of substantially anhydrous synthetic metal oxide gels which decrepitate when in contact with liquid water.

It is a further object of the invention to provide an improved process for the impregnation of synthetic metal oxide gels with aqueous liquids which contain an impregnating agent.

It is a further object oi the invention to provide an improved process for the impregnation of substantially anhydrous silica gel with certain aqueous compositions which render the resultant impregnated gel amenable to use as a dessicant, and as a catalyst ior a variety of purposes while minimizing crecrepitation.

It is still a further object of the invention to provide an improved process for the production of a dessicant grade silica gel which is impregnated with a moisture indicator such as cobaltous chloride.

The above objects, as well as others which will become apparent upon a complete understanding of the invention which is hereinafter fully described, are accomplished by subjecting a hygroscopic composition which will decrepitate when in contact with liquid water to the action of ice. It has been found that when hygroscopic compositions such as synthetic metal oxide gels and the like are admixed with ice in certain proportions, the resultant product will be a gel which is substantially hydrated with water. Such a hydration process is characterized by almost complete freedom from decrepitation or shattering of the initially dry gel composition. The hydroscopic compositions which may be treated with ice in accordance with the instant process include those solid, porous, synthetic gels which may contain only one metal oxide such as oxide of iron, aluminum, chromium, copper, zirconium, thorium, vanadium, manganese, silicon and the like, or mixtures of any of the said oxides which have been activated by a heating or calcining procedure to reduce the water content thereof. Also included within the term hygroscopic compositions are natural diatomaceous compositions such as fullers earth, infusorial earths and the like which have been calcined and/or acid treated in order to activate said compositions for use as catalysts, dessicants, etc. Such heated or calcined products are believed to contain internal stresses or strains which have been set up therein during the heating or calcining procedure. These physical properties of the dry materials are believed to cause the shattering or decrepitation of said materials when they are admixed with water or an aqueous solution of an impregnant. On the other hand, when such substantially anhydrous compositions are treated with ice in accordance with the instant process, the resultant hydrated product is substantially the same mesh size as the original product, and this mesh size is retained in any subsequent heating or calcining procedure which may be employed to reactivate the impregnated gel composition. A substantially anhydrous, porous gel or similar composition which has been treated with ice in a suitable amount in order to produce a hydrated product which will be substantially saturated with water when the ice has vaporized into the pores of the gel may be readily treated with solutions containing impregnating agents, and such impregnating treatment causes substantially no deformation or decrepitation of the hydrated product. The resultant impregnated hydrated product may then be treated in any conventional manner in order to produce the anhydrous impregnated product desired. In the event that a catalytic type of gel is required, the synthetic metal oxide gel which has been treated with ice may be admixed with a solution of a compound which is capable of forming a catalytic agent upon further chemical or physical treatment. This includes the addition of either acids or bases to the hydrated gel composition which contains a metallic compound as a result of the impregnation step. This treatment will cause the precipitation of the hydroxide or oxide of the metallic impregnant within the pores of the gel. The resultant impregnated hydrated gel may then be calcined at elevated temperatures in order to produce a substantially anhydrous catalytic agent. Alternatively, the hydrated gel composition which has been impregnated with a solution of a metallic salt may be heated directly at elevated temperatures, thereby decomposing the metal salt into the oxide thereof, accompanied by the volatilization of the anionic portion of the metal salt impregnant as gaseous by-products. This causes the deposition of the oxide of the particular metal in question within the pores of the gel. The instant process is also useful for the preparation of dessicant type metal oxide gels, for example, silica gel, by hydrating silica gel of a suitable mesh size by adding ice thereto in an amount sufiicient to cause the ultimate hydration of the gel. The hydrated gel may then be treated with a solution of a compound which will act as a moisture indicator. Cobaltous chloride is particularly adaptable to the production of dessicant grade silica gel in that when cobaltous chloridecontaining silica gel is substantially dry, the product has a blue tint. Upon becoming saturated with water, the product assumes a pink coloration.

More particularly the instant process is conducted by admixing a suitable quantity of ice with a hygroscopic composition of the type previously herein described, and which decrepitates when in contact with liquid water, in an amount which will cause sufficient hydration of the hygroscopic composition to prevent the shattering or decrepitation thereof when it is subsequently treated with a solution of impregnating agent. The hygroscopic metal oxide gel compositions which may be so treated include those metal oxide gels previously mentioned herein which contain not more than about 10% by weight of water. The amount of water which any particular gel will tolerate Without causing shattering of the gel during hydration with liquid water or other polar solvents such as methyl, ethyl and isopropyl alcohols will depend upon the particular metal oxide or oxides of which the gel is composed; upon the porosity of any particular gel; and upon the rate and extent of the removal of moisture therefrom during any prior heating and calcining procedure. In order to achieve the best results, a sufficient amount of ice should be added to the substantially anhydrous metal oxide gel, or to such a gel which contai s vnot more than about by .w it ite ate sea 'fl ly r suits will contain s men about and gel 'w 0am more than about 10% by ht of water yis preferably admixed with ts n amou t eiw enf ll an a t 1:00 wi e wei h 9 p sere irert 'w time io sis i e {th r u tant mistuie' e ed "to star; gmtil' the gel is -s ubstantially ut' t db water his ma ir u r a P l .loff' time between about :24 and about -96 hours,

' i "t 'aturje' surrounding i. 'th rart tu iie ,s re tedmixt re :i p ef ably naise ed c nta ner such a a ste d um.

"barrel or other suitable receptaclewhich s te ltiall seale rom the atmosph re. b t t not essent a t th operat on 9 th i s mess tha such a stora p oc d r b p s- Altem. ma a me a cxi es m be admixed wi h ice in he amount p v ou y herein .set 1forth'by employing a continuous procedure where th se1'-.,i,ce.niixt r p a ed 0 a su ab e nter is i .nism an i P mitted to fl rernain 'thereo a sufiicient length of time unti I at dwith e J-theh d ated eehhe nerer v uqus i mmthes stem- I completion of'thehydration of thehy- .groscopic metal (oxide gel compositions in aca l' mss bs ant a lrseii .cordance with vthe instant' process, the resultant hydrated .gel compositionlmay be then treated with a solution of .anysuitable active material or thepurposeof preparing any particular catalytic ag'ent, .dessicant' type .ge1 0r othercompo- .sition. For ,exanlp fi 9. hydrated gel .may' be treated with a colloidal soluti n of platinum .in accor anc w th-th o es s f rth i Pa e No. 1,g5 i7jl,1 .8 i3 issued vto W'. .A. Patrick, whereby :silica 'gel is impregnated with colloidal platinum. The .metal nexidelgel may also impregnated witha solutionofta water-soluble saltof a metal whose oxide "has catalytic properties. ,In -,-this class may be mentioned salts of metals such as copper, Vana'diurmhickel, aluminum and others. The amount ot impregnatir g agent ultimately de qs edin the h d ated .ge wil de en u o the concentration of thelmpregnatingsolution, upon the temperature of the mixture, upon the period of contact atime b'etwen the hydrated gel and impregnating solution, and upon the s e c .sr it 9 vth ,1 1h m en sol ion- .h resulting: sea :hyd te met wxid ee imay th mb rheat at l va ed temperatures i orde t ..ci ssmn th metal salt contained the gel, thereby producing a catalytic agent "deposited inthe'pores of the gel. Usuallyitemperatures betweenmabout 200 to 500 smarei uffici ntlor. thi murms Synthetic metal oxide gels, particularly silica gel, have been universally employed as dessicants in refrigeration systems, as well as in a dehydrating capacity for packaged products. When substantially anhydrous silica gel is treated with a solution of a compound which will act as a moisture indicator such as aqueous cobaltous chloride, an appreciable amount of shattering or decrepitation occurs for reasons hereinbefore set forth. This results in appreciable losses in the gel product. as the fines produced in this phenomenon must be removed from the gel in order {soproduce asa tisfactory, salabl'efpiiodifct." ever, when substan al ere" I treated with ice i "accordanc W e pr s ss asa t s cs iai i wiii'pbfind will act as am'oisture indicatorn'iay be added to the resultant hydrated gel and no appreciable hei in b dee ep iaiipn w nger-hi1 lo u A a resu t th ult mate dessi 'an' act in ha ub ta t al y ih sam e'sh' e as at i h rigyma hm wg l il s th enera aque us seli i r impre nating as h 'ireei i Q rniheimm ta b id el nd similar sensat ons. i sito t n 6 solvent other than water may be certain instances. For examplef heavy metal salts such those of, weathe are solubl n alcohols .andlet er'. Solutions of this typemayalso be emp loyedtfqr the impregnationof the gels. In $01119 it is useful to employ ,a mixture of w,a r Water-miscible organic solyentsfor the TD half tion of suitable impregnating-agents, and} methods are deemed to be \gwith ilil' thel cor ieof hem tant r ce s in order to more f,ully illustrate the .nature and character of the inventiombut .w i'th noin'; tention of being limited thereby, .the" follow rig e rampleis set forth:

Example silica ee s P e ared by ed esa t tween aboutfiandapouts z, ybymeight an The s bs ant allyu gel .was t en da s screening operation and a fraction of..gel..of ,.6 m sh to +l6 mesh was selectedfortheipreparation of adessicant materialf The silica. gel prepared as described aboYeswa-S admixedwil h about an equal ivighto'fficrushed ice and the resultant mixture pwas' tbrieaainia sealedpontainerfor about 48hou rs. TAiter 'th periodof time, theice had'disapp"aredIand gel .had become substantially .Is aturated Water. The hydrated gel was theniplaced tank and covered with an aqueous s o m cobaltous chloride. This' isoli tion ared by dissolving. cobaltous chloride in L130 550.- vide a solutionha iingqa gspecificlgra ty between bout 1.928 and about lines .QWni Yrias d".'la t F. The gel was allowed 'td'riiiaiififithe cobaltous chloride solution until a. sample, after draining and drying at a temperature of about 225 F., had a blue color equivalent to about 0.75 and about 1.25% by Weight of anhydrous cobaltous chloride. The main body of the impregnated gel was then removed from the cobaltous chloride solution and the excess moisture removed therefrom by centrifugation. The resultant product was then dried at a temperature between about 250 and about 450 F. for approximately to 1 hours. The resultant product contains a negligible amount of fines and has a more uniform particle size and color than cobaltous chloride gel which is produced by adding cobaltous chloride solution to substantially anhydrous silica gel or to partially dehydrated silica hydrogel.

The silica gel used in the above example may also be prepared by slowly adding in the form of a spray about 2 volumes of approximately 25% by weight sodium silicate solution to approximately 1 volume of about 20% by weight sulfuric acid, the latter being agitated during the addition of the sodium silicate solution. The gel may then be impregnated with the aqueous solution of cobaltous chloride as previously described.

While the above example illustrates the preparation of a silica gel dessicant, it is to be understood that the instant process is in no way limited thereto, but that any of the metal oxide gel compositions herein previously described ma be hydrated with ice in a similar manner, or one equivalent thereto. The resulting hydrated metal oxide gel may then be impregnated with compositions which will render the final products useful as catalysts, dessicants or for other purposes. Furthermore, the instant process is not limited to the specific procedural details recited herein but equivalent modifications and extensions of the factors herein set forth may be employed.

Having thus fully described the nature and character of the invention, what is desired to be secured by Letters Patent is:

l. A method of impregnating a hygroscopic siliceous gel with a solution of impregnant which comprises, admixing said gel with ice in an amount suflicient to produce a hydrated gel substantially saturated with water, permitting the resultant mixture to stand until the gel is substantially saturated with water and treating the resultant product with a solution of impregnant agent.

2. A method of impregnating a hygroscopic silica gel with a solution of impregnant which comprises, admixing said gel with ice in an amount sufilcient to produce a hydrated gel substantially saturated with water, permitting the resultant mixture to stand until the gel is substantially saturated with water and treating the resuliant product with a solution of impregnant agent.

3. A method of impregnating a hygroscopic siliceous gel with an aqueous solution of impregnant which comprises, admixing said gel with ice in an amount suificient to produce a hydrated gel substantially saturated with water, permitting the resultant mixture to stand until the gel is substantially saturated with water and treating the resultant product with an aqueous solution of impregnant agent.

4. A method of impregnating hygroscopic silica gel with an aqueous solution of impregnant which comprises, admixing said gel with ice in an amount suflicient to produce a hydrated gel substantially saturated with water, permitting the Number resultant mixture to stand until the gel is substantially saturated with water and treating the resultant product with an aqueous solution of impregnant agent.

5. A method of impregnating a hygroscopic siliceous gel with a solution of cobaltous chloride which comprises, admixing said gel with ice in an amount sufficient to produce a hydrated gel substantially saturated with water, permitting the resultant gel to stand until the gel is substantially saturated with water, and treating the resultant product with a solution of cobaltous chloride.

6. A method of impregnating a hygroscopic silica gel with an aqueous solution of cobaltous chloride which comprises, admixing said gel with ice in an amount sufiicient to produce a hydrated gel substantially saturated with water, permitting the resultant gel to stand until the gel is substantially saturated with water, and treating the resultant product with an aqueous solution of cobaltous chloride.

7. A method of impregnating a hygroscopic silica gel which contains not more than about 10% by weight of water, which comprises admixing said gel with ice in an amount sufilcient to produce a hydrated silica gel containing between about 40 and about of its weight of water, permitting the resultant mixture to stand until the silica gel is substantially saturated with water, and treating the resultant product with an aqueous solution of cobaltous chloride.

8. A method of preparing silica gel which will act as a humidity indicator, which comprises admixing silica gel of between about 6 and about +16 mesh size and which contains about 5% by weight of water, with about an equal weight of comminutcd ice; permitting the resultant mixture to stand until the gel is substantially saturated with water; treating the resultant hydrated gel with an aqueous solution of cobaltous chloride having a specific gravity between about 1.028 and about 1.043 at 100 F.; removing the cobaltous chloride solution from the hydrated gel when a sample of impregnated gel contains between about 0.75 and about 1.25% by weight of anhydrous cobaltous chloride, on a dry basis; and drying the resultant product at a temperature between about 250 and about 450 F.

OTIS W. ALLEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,798,766 Stoewener Mar. 31, 1931 2,324,518 Klein et a1 July 20, 1943 2,456,576 Bodkin et al Dec. 14, 1948 2,460,071 Davis Jan. 25, 1949 FOREIGN PATENTS Number Country Date 393,094 Great Britain June 1, 1933 

1. A METHOD OF IMPREGNATING A HYGROSCOPIC SILICEOUS GEL WITH A SOLUTION OF IMPREGNANT WHICH COMPRISES, ADMIXING SAID GEL WITH ICE IN AN AMOUNT SUFFICIENT TO PRODUCE A HYDRATED GEL SUBSTANTIALLY SATURATED WITH WATER, PERMITTING THE RESULTANT MIXTURE TO STAND UNTIL THE GEL IS SUBSTANTIALLY SATURATED WITH WATER AND TREATING THE RESULTANT PRODUCT WITH A SOLUTION OF IMPREGNANT AGENT. 